Spectroscopic analyzers and other instruments or equipment that rely upon measurements of absorption or emission of light (herein referred to generally as “spectrometers”) can be used in a broad range of applications for determining the presence and amount of one or more target analytes in a gas volume or flowing gas stream. Some spectrometers include a spectrometer cell, which can generally feature one or more optical components (e.g. windows or mirrors) for admitting light from one or more light sources and directing this light at least once through a sample of the gas prior to the light reaching a detector for quantifying absorbance, fluorescence or other emission, or the like resulting from interaction of the light with components of the gas sample.
In some applications, a gas volume or flowing gas stream being analyzed by a spectrometer can include chemically reactive compounds, which have the potential to interact in undesirable ways with various components of the spectrometer cell. In particular, optical materials and the optical coatings often used with optical materials in creating windows or mirrors for passing or reflecting light into a sample gas can be quite sensitive to contamination. As an example, optical materials and their optical coatings may be exposed to one or more of acidic and basic gases, liquids, chlorinated compounds, fluorinated compounds, high molecular weight compounds (which therefore typically have relatively low vapor pressures and a tendency to condense onto surfaces), etc., which can alter, influence, or otherwise affect the optical performance of such materials, potentially resulting in false or otherwise flawed spectroscopic analyses.
In addition, currently available sample cell configurations for use in spectrometers are generally not compatible with applications requiring operation over a wide range of temperatures. In particular with multi-pass sample cells that include one or more reflective optical elements, such as for example mirrors or the like, positioned to cause one or more beams of light generated by one or more light sources to be reflected within the sample cell (e.g. to increase a path length over which the one or more light beams travel within a gas sample contained within the sample cell), changes in temperature can require realignment of the reflective optical elements at the operating conditions.